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Biology A Guide to the Natural World Chapter 28 • Lecture Outline Communication and Control 2: The Endocrine System Fifth Edition David Krogh © 2011 Pearson Education, Inc. 28.1 The Endocrine System in Overview © 2011 Pearson Education, Inc. The Endocrine System • The endocrine system regulates bodily processes through hormones: substances secreted by one set of cells that travel through the bloodstream and affect the activities of other cells. • Each hormone affects only a select set of cells, known as a hormone’s target cells. © 2011 Pearson Education, Inc. The Endocrine System • Most hormones are produced and released by endocrine glands, defined as glands that secrete materials they have produced directly into the bloodstream or surrounding tissue. © 2011 Pearson Education, Inc. The Endocrine System • Some hormones are produced not by specialized glands, but by organs such as the kidneys or the heart. © 2011 Pearson Education, Inc. Hormones and Target Cells 1. Endocrine cells release hormone. 2. Hormone enters circulation. 3. Hormone is carried throughout the body. Hormone will not bind to cells that are not target cells 4. Binding occurs; receptor hormonal effects take place. target cell (skeletal muscle) © 2011 Pearson Education, Inc. Figure 28.1 pineal gland hypothalamus pituitary gland parathyroid glands (on posterior surface of thyroid gland) thyroid gland thymus gland cortex adrenal glands medulla pancreas testes ovaries © 2011 Pearson Education, Inc. Figure 28.2 The Endocrine System • Once secreted, hormones can take from several seconds to several hours to work, but then can continue to have effects for extended periods of time. • Given these timeframes, hormones tend to regulate processes that unfold over minutes, hours, or even years. © 2011 Pearson Education, Inc. 28.2 Hormone Types and Modes of Action © 2011 Pearson Education, Inc. Types of Hormones • There are three principal classes of hormones: • amino-acid-based hormones • peptide hormones • steroid hormones © 2011 Pearson Education, Inc. Types of Hormones • Each amino acid-based hormone is derived from a chemical modification of a single amino acid. • Peptide hormones (by far the largest class of hormones) are composed of amino acid chains whose lengths can vary greatly. © 2011 Pearson Education, Inc. Types of Hormones • Amino-acid-based and peptide hormones generally link to their target cells via receptors that protrude from the target cells’ outer or plasma membranes. • This binding initiates a chain of chemical reactions inside the cell that usually results in the activation of one or more enzymes. © 2011 Pearson Education, Inc. Types of Hormones • Steroid hormones generally pass through a cell’s plasma membrane and bind with a receptor protein inside the cell. • The combined steroid hormone/receptor molecule then binds with the cell’s DNA, thus turning on one or more cell genes, which results in the production of one or more proteins. © 2011 Pearson Education, Inc. Types of Hormones • Several steroid hormones, such as testosterone and estrogen, are reproductive hormones. © 2011 Pearson Education, Inc. The Endocrine System Animation 27.2: The Endocrine System © 2011 Pearson Education, Inc. 28.3 Negative Feedback and Homeostasis © 2011 Pearson Education, Inc. How is Hormone Secretion Controlled? • Almost all hormone secretion is controlled by negative feedback. • With its many negative-feedback loops, the endocrine system is important in preserving homeostasis, meaning an organism’s tendency to maintain a relatively stable internal environment. © 2011 Pearson Education, Inc. 28.4 Hormone Central: The Hypothalamus © 2011 Pearson Education, Inc. How is Hormone Secretion Controlled? • Endocrine activity is largely governed by the hypothalamus, which receives multiple sensory inputs and in response controls the release of multiple hormones. © 2011 Pearson Education, Inc. How is Hormone Secretion Controlled? • The hypothalamus exercises endocrine control by regulating hormonal release in three separate organs: • • • The adrenal glands The posterior pituitary gland The anterior pituitary gland © 2011 Pearson Education, Inc. How is Hormone Secretion Controlled? • Nerve signals that the hypothalamus issues to cells in the medulla of the adrenal glands bring about the secretion of adrenaline and noradrenaline. • Oxytocin and vasopressin (synthesized in the hypothalamus) are released into circulation within the posterior pituitary gland by axons extending from hypothalamic neurons. © 2011 Pearson Education, Inc. How is Hormone Secretion Controlled? • Hormones released by the hypothalamus go on to control the release of six hormones produced by the anterior pituitary gland, five of which go on to control the release of hormones by other glands. © 2011 Pearson Education, Inc. hypothalamus vasopressin Controls retention of water in the body by the kidneys kidneys anterior pituitary prostate gland in males oxytocin Stimulates contraction of uterus muscles and release of milk in females; assists in semen ejaculation in males posterior pituitary uterus and mammary glands in females medulla cortex adrenocorticotropic hormone (ACTH) Stimulates adrenal cortex to secrete glucocorticoids, which regulate energy use thyroid-stimulating hormone (TSH) Triggers release of thyroid hormones, which increase metabolic rate growth hormones (GH) Stimulates growth by prompting liver’s release of somatomedin hormones adrenaline + noradrenaline adrenal gland glucocorticoids T3, T4 hormones thyroid gland bone, muscle, other tissues prolactin (PRL) Stimulates mammary gland development and production of milk mammary glands follicle-stimulating hormone (FSH) Male: promotes sperm production Female: promotes egg development; stimulates ovaries to produce estrogen luteinizing hormone (LH) Female: produces ovulation; stimulates ovaries to produce estrogen and progesterone Male: stimulates testes to produce androgens testosterone testes estrogen progesterone ovaries © 2011 Pearson Education, Inc. Figure 28.6 28.5 Hormones in Action: Three Examples © 2011 Pearson Education, Inc. Insulin and Glucagon • The human body controls its circulating levels of glucose through the use of two hormones secreted in the pancreas: • insulin, a hormone that reduces blood levels of glucose • glucagon, a hormone that increases blood levels of glucose © 2011 Pearson Education, Inc. Insulin and Glucagon • Insulin is produced by the pancreas’ beta cells while glucagon is produced by its alpha cells. © 2011 Pearson Education, Inc. Insulin and Glucagon • After moving into circulation, insulin prompts cells to create channels through which they take in circulating glucose. • In liver and skeletal muscle cells, some of the glucose that is taken in may be stored in the form of a molecule called glycogen. © 2011 Pearson Education, Inc. Insulin and Glucagon • Glucagon prompts the transformation of glycogen back into glucose in skeletal muscle and liver cells. • Diabetes results from a failure of the body to move glucose into cells. © 2011 Pearson Education, Inc. (a) After a meal, the role of insulin glucose insulin glycogen glycogen beta cell glucose channel glucose muscle cell 1. Pancreas: Stimulated by high levels of glucose in the bloodstream, beta cells in the Islets of Langerhans produce insulin. 2. Other cells throughout the body: Insulin enables glucose to move from the bloodstream into cells by triggering the formation of channels in the cell membranes. liver cells 3. Skeletal muscle cells and liver cells: With insulin’s help, glucose can move into these cells and either be used right away or stored in the form of glycogen molecules. (b) In between meals, the role of glucagon glycogen glucose glycogen glucose glucose glucagon alpha cell 1. Pancreas: Stimulated by low levels of glucose in the bloodstream, alpha cells in the Islets of Langerhans produce glucagon. muscle cell liver cells 2. Skeletal muscle cells and liver cells: With glucagon’s help, glycogen is broken down into glucose. Muscle cells retain all the glucose they derive from this process, using it to power their own activities. Liver cells, meanwhile, move much of the glucose they liberate into general circulation. © 2011 Pearson Education, Inc. 3. Other cells throughout the body: Glucose released by the liver moves from the bloodstream into cells, supplying them with energy. Figure 28.8 Cortisol • The hormone cortisol, released by the adrenal glands, helps bring energy stores into use but also is a “stress” hormone that can have negative effects if stress goes on for extended periods. © 2011 Pearson Education, Inc. Table 28.1 Hormones of the Endocrine System: Their Sources and Effects Gland/Hormone Effects Hypothalamus Releasing hormones Inhibiting hormones Stimulate hormone production in anterior pituitary Reduce hormone production in anterior pituitary Anterior pituitary Thyroid-stimulating hormone (TSH) Adrencorticotropic hormone (ACTH) Follicle-stimulating hormone Tiggers release of thyroid hormones Stimulates adrenal cortex cells to secrete glucocorticoids Female: promotes egg development; stimulates ovaries to produce estrogen Male: promotes sperm production Luteinizing hormone (LH) Female: produces ovulation (egg release): stimulates ovaries to produce estrogen and progesterone Male: stimulates testes to produce androgens (e.g., testosterone) Prolactin (PRL) Stimulates mammary gland development and production of milk Growth hormone (GH) Stimulates growth by prompting liver’s release of somatomedin hormones Posterior pituitary Vasopressin Oxytocin Also known as antidiuretic hormone; controls retention of water in the body by the kidneys Stimulates contraction of the uterus muscles and release of milk in females; assists in semen ejaculation in males Thyroid T 3, T 4 Calcitonin Increase body’s metabolic rate Reduces calcium ion levels in blood Parathyroid Parathyroid hormone (PTH) Increases calcium ion levels in blood © 2011 Pearson Education, Inc. Table 28.1 (1 of 2) Table 28.1 Table 28.1 Hormones of the Endocrine System: Their Sources and Effects Gland/Hormone Effects Thymus Thymosins Stimulate development of white blood cells (Iymphocytes) in early life Adrenal cortex Glucocorticoids Mineralocorticoids Includes cortisol, which stimulates glucose production and breakdown of fats; a stress-response hormone Cause the kidneys to retain sodium ions and water and excrete potassium ions Adrenal medulla Adrenaline Noradrenaline Also known as epinephrine; stimulates release of energy stores; increases heart rate and blood pressure Also known as norepinephrine; effects similar to adrenaline Pancreas Insulin Decreases glucose level in blood Glucagon Increases glucose level in blood Testes Testosterone Ovaries Estrogens Progesterones Pineal gland Melatonin Promotes production of sperm and development of male sex characteristics Support egg development, growth of uterine lining, and development of female sex characteristics Prepare uterus for arrival of developing embryo and support of further embryonic development Establishes day/night cycle © 2011 Pearson Education, Inc. Table 28.1 (2 of 2)